Node

This node represents the basal ancestor to the Paranthropus clade. With the emergence of the Paranthropus lineage we can see the reemergence of a number of "primitive" features: The temporal lines are again marked by a strong anteromedial incursion, with males having a well-developed sagittal crest. Postorbital constriction has again increased. The glenoid fossa has increased in size and the foramen magnum is now heart shaped. The face is positioned high, relative to the frontal, and glabella is inflated. Facial dishing as well as maxillary trigon are present. The inferolateral orbital corner is not rounded and the orbital fissure is comma shaped. The zygomatic insertion at the alveolar border is set anteriorly at the P4 or anterior to it. Malar diagonal length is long. The incisor alveolar border is set close to the bi-canine line. The palate is thick, there is now overlap within the clivus and nasal floor, and incisive canal is developed. The nasal clivus itself is concave and the canine fossa is very much reduced. The molar enamel is hyperthick, and associated with this is the flat bun-odont occlusal morphology. In the mandible, the inferior torus is being developed, no metal foramen hollow, with a broad extramolar sulcus.

Emerging from this hypothetical ancestor is P. walkeri, in which parietal overlap occurs at asterion, and an asterionic notch is present. The compound temporal crests have reappeared and the glenoid fossa is shallow. The supra-glenoid width is extremely broad, and the external cranial base is extended. There is a reduction in cranial capacity and there is no occipitomarginal sinus. Mid-facial breadth is also extremely broad. Zygomatic insertion is low and the palate has increased in prognathism. The reemergence of many of these "primitive" features in P walkeri is of functional interest, and suggests either that it occupied a distinct dietary and/or habitat niche from that of its later daughter species from Kenya and South Africa (see below), or that the placement of Paranthropus is incorrect, and that homoplasy must be sought elsewhere in its anatomy. This example further emphasizes (if any is needed) the difficulty in trying to explain the developmental reasons behind observed morphological patterns. All such correlations must be considered tentative.

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